This invention relates generally to a lamp house for a photographic printer and more particularly, but not by way of limitation, to an additive tri-color lamp house used for controlling the exposure time of the additive primary colors in the lamp house thereby controlling the time to expose the light sensitive color print paper.
Heretofore, a common type a standard lamp house for a color photographic printer used a single white printing light source wherein the additive primary color filters were successively swung into the path of the light source. The disadvantage of this type of color printing was the total exposure time is relatively long.
An inherent problem in the exposure of conventional color print paper is the red sensitive emulsion layer on the print paper being less sensitive than the blue and green emulsion layers. Therefore, when making a color print from a negative, a longer red exposure time is required than either the green or blue exposure time. In the past this problem has been recognized and described in U.S. Pat. No. 3,950,093 to Schneider wherein the apparatus included three light emitters having an adjustable light intensity for increasing the exposure time on the color print paper. The subject invention does not rely on adjusting the light intensity but solves the problem of the unequal exposure times required on the light sensitive emulsion layers on the print paper by using controlled time exposure using both additive primary color filters and subtractive primary color filters.
Other color printers and lamp houses are disclosed in U.S. Pat. No. 3,492,070 to Zahn, U.S. Pat. No. 3,756,718 to Letzer and U.S. Pat. No. 3,923,394 to Frankieviecz. Also there have been prior art color printers that use fiber optic rods for conveying and mixing filtered light. These patents are U.S. Pat. No. 3,217,594 to Simmon and U.S. Pat. Nos. 3,825,335 and 3,825,336 to Reynolds.
None of the above patents discloses the structure of the subject invention having a lamp house including a combination of additive primary color filters and subtractive primary color filters in combination with light transfer rods to accomplish the advantages described herein.